Data from several cancer screening studies are being collected and analyzed to gain a better understanding of the impact and consequences of such screening in various population settings, and to develop new techniques for data analysis. Section staff are involved in various aspects of these studies, including design, monitoring and data analysis. The data base from the HIP breast cancer screening trial was used to address several scientific and modeling issues. Issues under investigation include the magnitude and duration of benefit, age- specific effectiveness, and application to model development. Data from the NCI sponsored lung cancer screening trials were analyzed. Investigations included assessment of incidence, staging, survival and mortality information. Monitoring continues of a trial to evaluate testing for blood in the stool for the early detection of colorectal cancer. Staff are also involved in several observational studies of screening procedures. In collaboration with investigators from the Centocor Company, the value of using the CA125 assay as a test for the early detection of ovarian cancer is being studied. Preliminary results indicate that the test may be useful in identifying a population of women at high risk for ovarian malignancy. Screening for bladder cancer in a high risk occupational cohort is under investigation in cooperation with DuPont Company staff. Data are being analyzed to relate disease characteristics and outcome to urine cytology and blood tests, smoking history and chemical exposure.